Photoacoustic spectroscopy (PAS) relies on the photoacoustic effect in irradiating a sample with intermittent pulses of light. Concomitantly, as the incident light hits the sample, heat is generated, and acoustic waves having a frequency relative to the light pulse frequency are generated. The resulting series of acoustic pulses is detected by a highly sensitive microphone (for example at lkHz repetition rate) and may be formulated into a signal for analysis and detection of chemical species.
Optical microphones rely on modulated light from a displaced or vibrating microphone membrane and detecting the modulation of the light. The modulated light pattern carries the displacement information that is provided by the microphone membrane. By knowing the stiffness of the microphone membrane, the displacement can then be translated into a known pressure signal.